1. Field of the Invention
The invention relates to a method for sawing a workpiece, and also to a device useful therefor.
2. Background Art
In order to saw a workpiece by slicing a multiplicity of wafers from this workpiece, wire saws are commonly used. Wire saws are suitable in particular for slicing a multiplicity of semiconductor wafers, solar wafers and other crystal wafers from a crystal piece in one working step.
The functional principle of such a wire saw is described in U.S. Pat. No. 5,771,876. Wire saws have a wire web, which is formed by a sawing wire which is wound around two or more wire feed or guide rolls. The sawing wire may be covered with a cutting layer, as disclosed in U.S. Pat. No. 6,390,896 B1. When using wire saws having a sawing wire without firmly bound cutting abrasive, cutting abrasive in the form of a suspension (slurry) is supplied during the slicing process.
During the slicing process, the workpiece, fastened on a table, passes through the wire web, in which the sawing wire is arranged in the form of wire sections lying parallel to one another. The passage through the wire web is brought about by means of a relative movement between the table and the wire web, induced by means of a forward feed device, which feeds the workpiece against the wire web (table forward feed) or the wire web against the workpiece.
Conventionally, the workpiece is connected to a sawing beam, into which the sawing wire cuts after having sliced through the workpiece. The sawing beam may for example be a graphite beam, which is adhesively bonded or cemented onto the circumferential surface of the workpiece. Lastly, the workpiece with the sawing beam is cemented onto the table. After slicing, the sliced wafers remain fixed on the sawing beam like the teeth of a comb and thus can be taken out of the wire saw. Subsequently, the remaining sawing beam is removed from the wafers.
It has been found that in the case of wire sawing, sawing grooves (sawing tracks) occur on the sliced wafers in the region of the wire exit. It is highly desirable to eliminate such sawing grooves or to minimize their number and size. No method which makes it possible to avoid these sawing grooves is known in the art.